I believe you read the Merger Plan incorrectly. If you go back to your link and read the entire paragraph, you will see that the language relating to Hospira that you quote in your first comment above falls under this language:

"any changes, effects, events or occurrences resulting from the following will not be deemed to constitute a Material Adverse Effect and will be disregarded when determining whether a Material Adverse Effect has occurred or is reasonably likely to occur"

so instead of stating that the action resulting from the Hospira litigation constitutes a Material Adverse Effect, the Merger Plan actually states the opposite: that any such action explicitly does NOT constitute a Material Adverse Effect.